Buffer Solution
A solution that resists changes in pH when small amounts of acid or base are added. It contains a weak acid/base and its conjugate in comparable concentrations.
Types of Buffer
| Type | Components | pH Range | Example |
|---|---|---|---|
| Acidic buffer | Weak acid + conjugate base (salt) | < 7 | CH₃COOH + CH₃COONa |
| Basic buffer | Weak base + conjugate acid (salt) | > 7 | NH₃ + NH₄Cl |
How an Acidic Buffer Works
When acid (H⁺) is added:
The conjugate base reacts with the added H⁺:
CH₃COO⁻ + H⁺ → CH₃COOH
The H⁺ is consumed, so pH barely changes.
When base (OH⁻) is added:
The weak acid reacts with the added OH⁻:
CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O
The OH⁻ is consumed, so pH barely changes.
📋 Exam Tip
In IB exams, you must explain the mechanism using equations. Simply stating "the buffer resists pH change" without showing which component reacts with the added acid/base will not get full marks.